Production of polyacrylonitrile filaments of high uniform density



May 26, 1959 I 2,888,317

E. F. EVANS PRODUCTION OF FOLYACRYLONITRILE FILAMENTS OF HIGH UNIFORM DENSITY Filed April 10, 1953 2iSheets-Sheet 1 DENSITY OF AIR, DRIED YARN gr./cc

TEMPERATUREC 0F 30 MIN. EXTRACTION ,ZNVENTOR Evan F. Evon ATTORNEY May 26, 1959 E. F. EVANS PRODUCTION OF POLYACRYLONITRILE FILAMENTS OF HIGH UNIFORM DENSITY 2 Sheets-Sheet 2 Filed April 10, 1953 0 8 6 4 2 I. H H

TEMPERATURE C OF DRYING FIG.3.

EXTRACTION TIME, MINUTES INVENTOR Evan F. Evan BY Z ATTORNEY United States PRODUCTION or POLYA'CRYLONITRILE r ms MENTS OF HIGH UNIFORMDENSIITY Eyan;F. Evaus, West Chester, Pa, as sig nor toiE. L du Po'ut .de Nemours and Company, Wilmington, Dela'corporationof Delaware This invention relates to improved shaped articles,

such as fibers, filaments, yarns and similar items and to r a process for producingthern; More specificallyjtheiin vention' is directed :to producing fiber structures .of' acrylonitrile,:homopolymers and of. acrylonitrile ycopolymers wherein ,the-acrylonitrile content is atuleast 85%, which structuresnaremore uniform than those produced heretoe fore, especially with respect to dyeabilityfly f 1 j ,1.

One-'method. of manufacturing polyacrylonitrile yarns isp'by :dry or evaporative spinning": of polymer solutions. The zyfll'll collectedzfrom the 1 spinning cell may contain upwards of; %solvent and frequentlyrat least- 30% solventu The recovery of the solventwis. essential for eco-i nomic operation, but the recoveryofthis residual solvent is-cornplicated by the factathatthe as spun. yarnmust undergo;;fur;ther processing to .provide it withfdesirable: textile properties. i 1 :r": 1 1;; I r. The, most important ,of these steps is drawing or, stretch-i ing to several times its as spun length, i.e. from .210 10 times or more. The condition of the yarn as it is subjected to this stretch is ..all important if optimumproperties are to be attained in the drawn product. One of the essential requirements for uniformityof results is a'low and uniform solvent content of the yarn entering the ste am stretching chamberp The remova'l'of solvent from-"the spun yarn can be accomplished by water or aqueous liquor washing and this has beendone very successfully by pressure washing wound packages of the: yarn. i

T he reriioval of solvent from the yarn by washing with v? cold water, however, produces a porous structure of low" density. It was found that this excessive porosity, which is undesirable, could be largely gavoid ed by Washing with short 'length deep-dyeing flashes to. the fabric 'madei 60 therefore, an object of-this invention to provide a novel process forthe .production of;yarns,;filaments, fibers'and like'structures of acrylonitrile homopolyrners or of copolyr'ners wherein the aorylonitrile 'content at least 85%", which'structures' are characterized 'by more uniform 'dyeability, Other objects of this invention will. be apparent from the descriptionthat follows, i

' i he o bjects'pf this inventio nar'e accomplishedby spin l tween about 2% and about 4% by weight.

2 ,888,31 Patented May 26,

the structure with an aqueous liquid at a temperature below about 50 C. until the solvent content of the structure is no more than about 2.5% by weight (based on the dry weight of the structure), drying thejstructure at a temperature below about 110 C. to produce'a substantially undrawn structure containing no more than 7% by weight of water andthereafter drawing 2 tor'10 times or more. The stretching or orientation step is usually accomplished at an elevated temperature, 'for'example, at 100 C. or above. Preferably, the water content is be- Figure'I shows the effect of the;terriperatureirsed,in the extraction on the density of undrawn yarn ai dried zselc v.Ji V

Figure II shows'th'e effect 'of thedrying temperature on the density of undrawnyarn which has been solvent extracted at a temperature below 40 C.; and

Figure III shows the effect of thejtiin ofextraction on the density of air dried yarn. v; 1, I

Washing of the filamentary structuresinay be accomplished with water or with a dilute aqueous solution of a solvent, usually thatused in the spinninglsol-ution.

washing-*may 'be used": It may be washedonthe runhby'j leading it throughbn'e' or more troughs *containingfthe' s nking or similar methods.

methods or combinations of methods may 'als fb 'g di Drying may be carried out Warm air drying is very satisfactory as is lio't'roll dryiii-g;

washing liquor or under showers of washin'gliquorj II'I" the-form of sk'eins or in other readily accessible the structures may be subjected to'solventextraction byj Other washing lt is important that the temperature of-th wash liqu be maintained below about 50* C'. 'I 'he' wash-liquoli temperature maybe substantially below this; level and even below room temperature, i.e. at -5 'CE *or less;'"

although there'i's no advantage in coolingthe-wa'shfliquof" below room temperature. Generally, temperatureslinthe' range-of from room temperature to about 40- C will be found most satisfactory. 1 r

in a number{ if-' ways.

provided the air or roll temperature isnot -allowed to exceed about 110 C. While excellent results'have been obtained by air drying at room temperature, drying' at temperatures above about 70 C. 'is preferred. 1 Itfisinr f poirtant to dry down to below about 7% moisture content of the yarn and preferably to about 2% to 4% 'mbi'st'ure: With increasing )amounts of moisture'above' 7% "'th re-- sultant yarns dye less and less uniformly:-

A bit is indeed surprising thatthe combination of critical low temperature solvent extraction withcriticalfdryifigf produces a high density structure whichis very much;

improved in uniformity of densitysince low temperature, solvent extraction without drying results in a prawn;

, yarn of very low density, i.e. of the order oflrll 'orless.' 7 While high temperature C.) solvent extraction'fol lowed by high temperature C.) dr'ying gives-high" density yarn structures, the density uniformity-is not drawingand still greater density non-uniformity Tablel I below shows comparative figures on deusities,.of:lyarns after. extraction: and. drying in accordance with-thermalltion but before drawing and the standard deviation TABLE I Extrac- Drying Standard tion Temp, No. of Average Devia- Tenp C. Samples Density tion To compare density values of some drawn yarns under different conditions of processing, Table II below is given. It will be noted here too that there are some changes in densityin undrawn versus drawn yarn.

TABLE II Extrac- Density tion Drying Temp., Temp.,

0. 0. Before 8X Drawn Drawing Yarn 25 undried 100 25 100 undried oflthe greaterdensity as is shown in Figure II. In this figure density curves again are plotted, this time on data resulting from low temperature (below 40 C.) aqueous extraction of solvent from the as spun yarn after which the ashed yarn is dried at temperatures ranging fro rn 40 C. to 135 C. One set of data plotted is on yarn dried under just sufficient tension to maintain its wet. length (curve C) while the other set of data is on yarndriedwithout any tension (curve D); Here it will be noted the curves coincide in temperatures above 80 Crand variations in tension as may develop in drying yarn will not cause substantial differences in density when the yarns are dried at temperatures above about 70 C. Forthis reason, temperatures between 70 and 110 C. are preferred.

Another set of data showing the desirability of low temperature extraction over higher temperatures of extraction for a period of time ranging from one second up to several hours is shown by the curves in Figure III. Herein it is notedithat the time of extraction at 25 C.

hasno effect on the density of the yarn, whereas at 60,

75 f and 1100-." C., the time of extraction importantly affects; the density of. the yarn. Thus, by conducting solvent extractiomata low temperature and following this step by drying, preferably at a temperature between 70 and 110 C.,, t h e density of the resulting yarn before and after drawing will be relatively high and more uniform than obtainable under other operating conditions. While uniform-density yarn per se may not result in uniform dyei'ngiyarn; it appears from the data collected that uniform dyein g yarn cannot be secured without uniformity of yarn density.

In theexamples that follow additional illustrations of to eight times the undrawn length and the resulting draw- Example I A 640 denier-40 filament yarn produced by evaporative spinning of an acrylonitrile homopolymer from solution in N,N-dirnethylformamide was wound up at the spinning machine on a perforated core. This yarn contained about 40% solvent (based on the dry solvent-free weight of the yarn) and was subjected to solvent extraction by pressure washing with water at room temperature. The washed yarn was skeined and dried at room temperature on swifts which allowed the yarn to shrink upon drying. The dried yarn was subjected to steam drawing to eight times its dry undrawn length followed by 9.5% hot relaxation. A piece of tubing knitted from this yarn and dyed with a Celanthrene Pure Blue BRS was free of dyeing non-uniformities.

Example II 475 denier-30 filament acrylonitrile homopolymer yarn dry spun from solution in N,N-dimethylformamide and collected on perforated cores while it contained about 35% solvent (based on the dry and solvent-free weight of theyarn) was pressure washed with water containing 2% N,N-dimethylformamide for 2 hours, at the end of which time the solvent content of the yarn had been reduced to about 2% (based on the dry weight of the yarn). The yarn was subjected to drying by means of heated rolls, varying the roll contact and the temperature of the rolls to produce samples having different moisture contents as they were subjected to pressure steam drawing. The steam pressure was varied to give good drawing ing tensions are recorded with the other data in Table III below. After drawing, the yarn was heat relaxed TABLE III Percent Steam Drying Roll Moisture Draw Pressure Sample Roll Con- Content Dyeing Ten- For Temp., tacts of Dried Uniformity sion, Drawing,

C. Yarn Grams Pounds] Sq. In.

85 12 3. 8 good 30 55 85 21 2. 9 excellent. 30 44 85 21 0 40 30: 30 30 32 80 30 50 110 9 32 54 It will be noted that all samples dried to below 3% moisture at 80 to C. showed excellent dyeing uniformity, the dye test being on knitted tubing dyed with Celanthrene Pure Blue BRS.

Example III Acrylonitrile homopolymer yarn dry spun from solution in N,N-dimethylformamide and collected on a perforated core as 510 denier-30 filament yarn containing about 35% solvent (based on the dry and solvent-free weight of the yarn) was pressure washed with water at.

a temperature of 40 C. for 3 /3 hours at which time the solvent was reduced to about 1.8% (based on the dry and solvent-free weight of the yarn). This yarn was then dried on the run by passing it twelve times around the.

contact drying roll heated to 97 C. to reduce the moisture content of the yarn to about 2.9%. It was drawn eight times, in a steam drawing chamber and thereafter the yarn was heat relaxed 10%. The drawn yarn had a density of 1.179 and comparable physical properties;

to yarn prepared by hot water washing and drawing withjunctions where the yarnfromthe outside of the spinning package joined yarn from the inside of the same or different spinning package. A control yarn was similarly produced, except that it was washed at a temperature of 105- C. and was drawn without drying; in dyeing tests there were a number of short length deep dyeing flashes, especially in yarn-from the outside of the spinning cake and a distinct dye junction between inside and out side yarn, the inside yarn being'lighter. Also, yarn was subjected to the same step of solvent extraction but dried before drawing by contact, with rolls heated to 130 C.; this reduced the moisture content of the yarn to below 2% and non-uniform dyeing yarn, similar to the contr'ol 'yarn resulted.

1 ExamplelV i A copolymer of acrylonitrile and methylacrylate 94/6 was dry spun from solution in N,N-dimethylformamide and wound up as 510 denier-30 filament yarn containing about 30% residual solvent. The yarn was trough extracted in countercurrent flowing water at 30 C. and then dried at room temperature. The dried undrawn yarn had a density of 1.181. It was pressure steam drawn eight times and then hot relaxed 12% to give a deep and uniform dyeing yarn free of short length variability.

Example V An acrylonitrile homopolymer dry spun yarn which was subjected to continuous trough extraction in countercurrent flowing water at 25 C. followed by 90 to 110 C. roll drying and thereafter steam drawn and relaxed showed good dyeing uniformity, whereas yarns similarly trough extracted with water at temperatures of 25 C. and 95 C. and steam drawn without previously drying exhibited very non-uniform dyeing. Also, yarns trough extracted at 95 C. followed by 90 or 110 C. roll drying before steam drawing exhibited non-uniform dyeing.

Example VI Acrylonitrile homopolymer dry spun yarns were collected at the spinning machine on perforated cores in the form of square ended packages with the aid of self-traversing rolls. These packages were effectively pressure washed with water or aqueous liquor containing up to 3% solvent (N,N-dimethylformamide) at temperatures of from 20 C. to 40 C. and thereafter dried on 95 C. rolls before steam drawing and hot relaxing. This yarn drawn eight times exhibited good dyeing uniformity, whereas yarn similarly extracted but dried on 125 C. rolls displayed numerous non-uniformities in dyed knitted tubing.

In other tests it has been shown that solvent extraction from dry spun acrylonitrile homopolymer yarn at 30 C.followed by drying at the same temperature, the yarn being free to shrink during both treatments, resulted in isotropic shrinkage of the yarn, this shrinkage being the result of the decrease in yarn volume due to its solvent loss. In contrast, hot extraction followed by drying, hot or cold, resulted in greater longitudinal shrinkage than the isotropic value. It follows then that by the practice of this invention, yarns of more uniform denier can be obtained as well as improved uniformity in dyeing.

Copolymer yarns wherein the acrylonitrile content is at least 85% behave in general much the same as the homopolymers. For instance, water extraction for one hour of acrylonitrile/methyl-acrylate 94/ 6 copolymer yarn dry spun from solution in N,N-dimethylformamide showed a maximum air dried density of 1.181 when extraction was at 29 to 48 C., while extraction at temperatures above 60 C. gave lower and variable air dried density. At 60 C. extraction, the density was 1.143; at 70 C., 1.137; at 79 C., 1.121 and at 90 C., 1.137.

However, in some instances an acrylonitrile copolymer yarn is more detrimentally aifected by high temperature extraction than is the homopolymer yam. For example, an acrylonitrile/methylacrylate 94/6 copolymer yarn was found usdevelop' numerous cracks the' yaffi core or show separation' of the yarn skin from theyarnz core (shown by microscopic dyed cross-sections),"d'e-" pending on spinning and packaging history. On the other hand, low temperature extraction with anattendan't' slow-"1 er extraction rate, did not develop any skin/core interde-' are indeed important if not essential for the continued 1 commercial acceptance of t ya n. Short lengthdyeihg flashes have been present 'in-more-or-jless pronoiinced" form and to a greater or lesser extent since the beginning of manufacture of acrylonitrile polymer yarns. As earlier stated, a change in density from 1.17 to 1.14 causes a very decided change in dyeing depth and even a density change of as little as 0.01 is suflicient to bring about a change in depth of color. This invention enables the production of much more uniform density yarn than has been produced heretofore, in many cases with maximum density variation within a single yarn package no greater than about 0.005, and as a result discernible dye differences are substantially eliminated. The process of this invention can be applied effectively to the many acrylonitrile polymers and copolymers disclosed in such patents as US. 2,404,714 to 2,404,727. These contain a major amount of acrylonitrile and those of most interest are those that are derived from about or more, by weight, of acrylonitrile.

Generally, packages having unsupported side walls are made. High temperature extraction of these results in package instability and deformation, but by the process of this invention these adverse elements are avoided. In addition to this, difi'erences between inside and outside densities are decreased and dyeing uniformity is attained.

Any modification which conforms to the principles of the invention described herein is intended to be included within the scope of the claims below.

I claim:

1. A process for the production of a filament of high uniform density composed of at least 85% of acrylonltrlle which comprises producing by dry spinning a substantially undrawn filament containing at least about 5% of a solvent, based on the dry weight of said filament, by extrusion of a solution of said polymer in said solvent; washing said filament with an aqueous liquid at a temperature below about 50 C. until the solvent content 1s below about 2.5%, based on the dry weight of said filament; and drying the resultant, extracted filament at a temperature from about 70 C. to about C. to produce a substantially undrawn filament containing no more than about 7% of water, based on the dry weight of said filament.

2. A process in accordance with claim 1 wherein said water content is reduced to about 2% to about 4% based on the dry weightof said filament.

3. A process in accordance with claim 1 wherein said washing produces an extracted filament having less than 2% residual solvent.

4. A process in accordance with claim 1 wherein the temperature of the said aqueous liquid is in the range of about 5 C. to about 40 C.

5. A process in accordance with claim 1 wherein said polymer is polyacrylonim'le. i

6. A process in accordance with claim 1 wherein said polymer is a copolymer.

7. A process for the production of a filament of high uniform density composed of at least 85% of acrylomtrile which comprises producing by dry spinning a substantially undrawn filament containing at least about 5% of a solvent, based on the dry weight of said filament, by extrusion of a solution of said polymer in said solvent;

washing said filament with an aqueous liquid at a temperature below about 50 C. until the solvent content is below about 2.5%, based on the dry weight of said filament; drying the resultant, extracted filament at a temperature from about 70 C. to about 110 C. to produce a substantially undrawn filament containing no more than about, 7% of water, based on the dry weight of said filament; and stretching the resultant extracted, dried fila ment to produce an oriented filament.

8. A process in accordance with claim 7 wherein said polymer is polyacrylonitrile.

9. A process in accordance with claim 7 wherein said polymer is a copolymer.

10. A process in accordance with claim 7 wherein said resultant extracted, dried filament is stretched at least twice its original length.

11. A process in accordance with claim 7 wherein'said water content is reduced to about 2% to about 4% based on the dry weight of said filament.

12. A process in accordance with claim 7 wherein the 1 said resultant, extracted filament has less than 2% residual solvent.

13. A process in accordance with claim 7 wherein the temperature of the said aqueous liquid is in the range of 1 about 5 C. to about 40 C.

References Cited in the file of this patent UNITED STATES PATENTS Jones et a1. Sept. 4, 1956 

1. A PROCESS FOR THE PRODUCTION OF A FILAMENT OF HIGH UNIFORM DENSITY COMPOSED OF AT LEAST 85% OF ACRYLONITRILE WHICH COMPRISES PRODUCING BY DRY SPINNING A SUBSTANTIALLY UNDRAWN FILAMENT CONTAINING AT LEAST ABOUT 5* OF A SOLVENT, BASED ON THE DRY WEIGHT OF SAID FILAMENT, BY EXTRUSION OF A SOLUTION OF SAID POLYMER IN SAID SOLVENT; WASHING SAID FILAMENT WITH AN AQUEOUS LIQUID AT A IS BELOW ABOUT 2.5%, BASED ON THE DRY WEIGHT OF SAID FILAMENT; AND DRYING THE RESULTANT, EXTRACTED FILAMENT AT A TEMPERATURE FROM ABOUT 70*C. TO ABOUT 110*C. TO PRODUCED A SUBSTANTIALLY UNDRAWN FILAMENT CONTAINING NO OF SAID FILAMENT. 